Billing Header Text Variable

Hi,

I have generated a SO10 standard text including variables from VBRK tables.
For example: 'Sample text with: &VBRK-KUNAG&.'

I made the required setting by transaction VOTXN.

1-When I generate a new VF02 billing record, this SO10 text object is succesfully copied to header text, but without

variable value:

"Sample text with: ."

2-When I send this record to EDI I can see the EDI text just as SO10 text object:

'Sample text with: &VBRK-KUNAG&.'

Meanwhile, I can see this text with the variable value in the output program without any problem.

"Sample text with: 32881."

How can I transfer this variables in header text and EDI corectly?

Thanks,

Hamza